GROWTH IN TREES. 



37 



GROWTH OF A BEECH TREE. 



An instrument with a floating frame of bario of the U-form was 

 put in place on a beech tree (Fagus grandifolid) on the grounds of 

 Johns Hopkins University at Baltimore on April 16, 1919, about the 

 time development of the leaves was beginning. In addition to the 

 somewhat irregular daily variations swellings were seen as a conse- 

 quence of rains with subsequent shrinkage. Not until May 18, when 

 the tree was in full leafage, did some increase show in the record. 

 This continued until May 30, after which equalizing variations ensued, 

 which continued until mid-July. A week of rains was followed by 

 enlargements which continued for a month and had a net total of 

 about half that of the spring growth in May and June. 



Now followed a period of regular equalizing daily variations, which 

 terminated about September 14. The ensuing enlargement, which 

 lasted for 3 weeks, showed a total increase less than hi the preceding 

 active period. Only equalizing variations were now seen and the in- 

 strument was dismounted early in October. The total accretion to 

 the diameter amounted to about 4.5 mm. (fig. 15). 



EQUALIZING DAILY VARIATIONS IN DIAMETER. 



The equalizing changes in the trunk are such that the diameter is 

 least at midday or in the afternoon, when the temperature of the trunk 

 is highest. The difference between the readings of a thermometer 

 thrust under the bark in early morning and at noontime is never more 

 than 8 C. or at most 10 C., while that in the center of the trunk may 

 be no more than a degree or two. Whatever the temperature might 

 be, a rise would tend to expand the woody column. Dendrographic 

 and other measurements show a decrease at this time. The trunk is 

 seen to shrink at a time when the temperature is highest. It is obvious, 

 therefore, that we must look to causes other than a direct temperature 

 effect. 



The first possibility to be tested was that of the water relations of the 

 bark, and Monterey pine No. 7 was chosen for this purpose. A small 

 section of bark and bast was removed from the north side of the tree 

 below the instrument, and these two formations were separated and 

 placed under the auxographs in the dark room in which swelling liquids 

 now stood at 12 C. The results are as below: 



